Heat-developable light-sensitive materials are known in the field of art and heat-developable light-sensitive materials and processes for processing them are described, e.g., in Shashin Kogaku no Kiso (The Basis or Photographic Engineering), "Non-Silver Salt Photography", pages 242 to 255, published by Corona Sha, (1982).
Also, various processes of obtaining color images by heat development have been proposed.
For example, a process of forming color images by the combination of the oxidation product of a developing agent and a coupler is described in U.S. Pat. Nos. 3,531,286, 3,761,270, and 4,021,240, Belgian Patent 802,519, and Research Disclosure (hereinafter referred to as RD), (September, 1975), pages 31 to 32.
However, since the aforesaid heat-developable light-sensitive material for obtaining color images is of a non-fixing type, silver halide remains therein after forming images, which causes a serious problem that when the color images are exposed to intense light or stored for a long period of time, the background is gradually colored. Furthermore, the aforesaid processed have disadvantages that the development requires generally a relatively long period of time and images obtained have high fog and a low image density.
For solving these problems, a process of imagewise forming or releasing diffusible dye(s) by heating and transferring the diffusible dye(s) onto an image-receiving material having a mordant by using water or other solvent is disclosed in U.S. Pat. Nos. 4,500,626, 4,483,914, 4,503,137, and 4,559,290 and JP-A-59-165054 ("JP-A" as used herein mean an "unexamined published Japanese patent application").
However, in the aforesaid process, the development temperature is high and the light-sensitive materials being employed are yet insufficient in storage stability.
Thus, a process of carrying out heat development in the existence of a base or a base precursor and a slight amount of water to form dye(s) and transferring the dye(s) thus formed, whereby the development is accelerated, the development temperature is reduced, and processing is simplified, is disclosed in JP-A-59-218443 and JP-A-61-238056 and European Patent 210,660A2.
Also, various processes obtaining positive color images by heat development are proposed.
For example, U.S. Pat. No. 4,559,290 discloses a process of using a so-called DRR compound which has been converted into an oxidized type compound having no faculty of releasing a dye and a reducing agent or a precursor therefor, oxidizing the reducing agent by heat development according to the exposed amount of silver halide and reducing the aforesaid compound with the reducing agent which remained without being oxidized to release a diffusible dye.
Also, EP-A-220746 and Kokai Giho, 87-6199 (Vol. 12, No. 22) describe heat-developable color photographic light-sensitive materials using a compound capable of releasing a diffusible dye by a reductive cleavage of an N-X bond (wherein X represents an oxygen atom, a nitrogen atom or a sulfur atom) as a compound capable of releasing a diffusible dye by the same mechanism as described above.
However, the aforesaid heat-developable color photographic light-sensitive materials giving positive color images are not in the level of commercially available color print materials in the stains, and tone reproducibility of color images formed.